1. Field of the Invention
The invention relates generally to electromagnetic relays and more particularly to an electromagnetic relay with a tilting-armature pivoted about a knife-edge bearing.
2. Description of the Prior Art
In the art of electromagnetic relaying, relay devices having an armature supported by and pivoted about a knife-edge bearing are known as tilting-armature relays. In this type of relay, an armature is mounted above a magnetic core wrapped with an excitation winding. The magnetic core and excitation winding are partially enclosed by a magnet yoke which includes an edge. The armature includes a notch at one end which is positioned above and mates with the edge of the magnet yoke. A supporting spring is employed to apply a pulling force on the armature against the edge of the magnet yoke causing the armature to pivot about the edge. This action may be employed to control the operation of a set of electrical break contacts. It is known to utilize support springs comprised of metal tapes or spiral springs as is illustrated in the Swiss Pat. No. 20 68 32 and the German Published Patent Application No. 20 29 607. In addition, German Pat. No. 30 08 783 discloses supporting springs fashioned from plastics material and molded for example to a coilform. It is common in each of the disclosures recited that the bearing and resetting or restoring force produced by the supporting springs and acting upon the armature depends upon the spring force of the supporting spring. However, in mass production, a desirable spring characteristic can only be produced within certain tolerance limits. The tolerance limits exist due to the method of manufacturing the supporting springs and the quality of material utilized. Note that the metal tapes and spiral springs do not always have exactly the same resilient properties throughout their entire lengths. Therefore, a problem exists in that the resetting or restoring forces acting on the armature are subject to fabrication spreads. The restoring force acting on the armature is most significant when the excitation coil is not energized forcing the armature to pivot into a rest position. The set of electrical break contacts which are employed to control an external electrical circuit are closed in the rest position. The restoring force acting on the armature controls the pressure between the break contacts and consequently the quality of the electrical connection. Thus, if the restoring force is not constant, then the contact pressure varies resulting in a poor electrical connection. These problems continue to exist in the art of building tilting-armature relays.